This invention relates to shoe manufacture and, particularly, to improvements in reinforcing and stiffening portions of a shoe, such as the shank region of an insole which extends from the heel to the ball portion. The invention relates to improvements and articles for forming a shank stiffener of the type disclosed in U.S. patent application Ser. No. 765,096 filed Feb. 3, 1977 and which is assigned to the assignee of this application. That application discloses techniques and articles for forming shoe shanks, the article being in the form of an elongate shank strip or rope having a carrier sleeve which contains a plurality of fiberglass strands in a thermosetting plastic resin matrix. The thermosetting matrix is activatable in response to a selected external stimulus such as, for example, radiant heat. The sleeve preferably is formed from a material which is transparent to radiant energy to permit radiant activation of the resin in situ on the insole bottom. The shank thus formed adheres to the insole bottom by way of a variety of means, including but not limited to, melting of the sleeve to form an adhesive bond, direct contact between the resin matrix and the insole, application of an adhesive layer between the shank strip and the insole or a combination of these.
The aforementioned patent application discloses an improved sleeve construction in which the sleeve is formed from a first, upper sheet and second, lower sheet or strip which may be of a different material. The upper and lower strips are attached to each other along their longitudinal edges which define the margins by which the sleeve is to be handled. The upper strip is substantially transparent to the radiant energy to permit the resin to be activated. The upper strip is formed from a material which will not deteriorate or otherwise lose its strength from exposure to the radiant heat or from exothermal heat generated during the curing process, at least until the resin has assumed a substantially final shape. The lower, insole-engaging sheet preferably is thermoplastic and will melt under the influence of the applied and/or exothermal heat to serve as an adhesive bond between the cured shank strip and the insole bottom. By way of example, the upper sheet may be formed from a polyester film such as Mylar and the lower sheet may be formed from polyethylene.
It is desirable that the margins extend laterally and in a substantially flat configuration so that they may be easily and conveniently held, gripped or otherwise manipulated. However, because of the dissimilarities in the properties of the polyester and polyethylene film, it may sometimes occur that the margins tend to curl, rather than extend laterally in a generally straight or flat configuration, as desired. When the margins curl, that makes it somewhat difficult and awkward to handle the strip by its margins. Curling of the margins may result from any of a number of causes, for example, from the heat sealing of the marginal portions of the strip, or from feeding or tensioning of the sheets during the manufacturing process. The present invention relates to an improved configuration for the margins which reduces the tendency for the margins to curl and which results in substantially flat, well-defined and projecting margins which may be easily gripped and handled.
In brief, the present invention resides in modifying the marginal portions so that they are doubled over and folded so that the top and bottom surfaces of each of the margins are defined by the first sheet, with the polyethylene portions of the margin being sandwiched and fused between the polyester material of the first, top sheet.
It is among the general objects of the invention to provide an improved shank strip of the type described.
A further object of the invention is to provide a shank strip of the type described in which the margins display little curling tendency.
Another object of the invention is to provide a shank strip of the type described in which the margins remain substantially flat and protrude substantially laterally of the shank strip to facilitate the strip being handled by its margins.
Still another object of the invention is to provide an improved elongate shank stiffener of the type described having a curable resin surrounded by a carrier sleeve and in which the sleeve has upper and lower surfaces formed from dissimilar materials, provided further with heat sealed, but uncurled margins.